What should I check first if my HP Z240 Tower Workstation has no power, no boot, or no video?

First, check that the computer and monitor are plugged into a working electrical outlet and that both power lights are on. Also verify the voltage select switch (on some models) is set to the correct voltage for your region (115V or 230V), and check all cable connections for loose or incorrect connections. If the system remains in sleep mode, press and hold the power button for at least four seconds to shut down, then press it again to restart. (Page 25)